This invention relates to track tensioning and recoil systems, and more particularly, to such a system which utilizes cylinder means and a sleeve piston associated therewith for movement therein.
In track-type vehicles, it is well known to provide movement of a front idler toward and away from a rear drive member so that (i) the track entrained thereabout may be properly tensioned between the front idler and the rear drive member and/or (ii) recoil of the front idler may be allowed. In a conventionally designed vehicle, recoil is allowed by means of a resilient spring which is compressed at the same rate of movement as the actual recoil movement of the front idler toward the rear rotatable member (see, for example, U.S. Pat. No. 2,887,342 to Helsel). While such systems are generally effective, it is to be noted that, because spring compression movement is equal to recoil movement, a relatively large, stiff spring must be used (i.e., if spring travel could be designed as greater than the corresponding amount of recoil movement, a smaller, less stiff, and consequently less expensive spring, with greater impact load recoil capacity, could be used).
Examples of systems which achieve different rates of movement are shown in U.S. Pat. No. 3,493,124 to Thompson, U.S. Pat. No. 3,574,418 to Okabe, and U.S. Pat. No. 3,539,229 to Scully. However, it is to be noted that the Thompson device achieves less spring compression than the corresponding recoil movement, so that, for good performance, a very stiff, heavy spring would have to be used in this place, which is exactly the opposite of the aim of this invention.
The Okabe and Scully devices do indeed provide greater spring movement than the corresponding recoil movement. However, the Okabe device achieves this by use of an annular ring-type piston, which requires sealing on both the inner and outer surfaces thereof, and in addition may be subject to possible skewing, since such piston is of relatively large diameter. And the Scully device includes a wall with a valve therein preventing compression of the spring until a certain, predetermined pressure on the valve is achieved.
Of more general interest in this area is U.S. Pat. No. 3,343,889 to Bexten.
U.S. Pat. No. 3,829,172, assigned to the assignee of the present invention, discloses a system which achieves greater spring compressive movement than the corresponding amount of recoil of the front track frame portion toward the rear track frame portion. Such system utilizes a pair of pistons of different diameter, each sealingly engaged in a bore of a member, and such member and pistons together define a chamber within which substantially incompressible fluid is disposed. While such a system has proved relatively effective in operation, it will be understood that improvement in the operating efficiency and design of such a structure are always being sought, especially in view of the fact that each piston of that patent must be sealingly associated with such member with which it is slidably associated.